Commit ba3dd36c authored by Peter Zijlstra's avatar Peter Zijlstra Committed by Ingo Molnar
Browse files

perf: Optimize hrtimer events 



There is no need to re-initialize the hrtimer every time we start it,
so don't do that (shaves a few cycles). Also, since we know hrtimers
run at a fixed rate (nanoseconds) we can pre-compute the desired
frequency at which they tick. This avoids us having to go through the
whole adaptive frequency feedback logic (shaves another few cycles).

Signed-off-by: default avatarPeter Zijlstra <a.p.zijlstra@chello.nl>
LKML-Reference: <1297448589.5226.47.camel@laptop>
Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
parent 163ec435

kernel/perf_event.c

+32 −3
Original line number Diff line number Diff line
@@ -5602,6 +5602,10 @@ static enum hrtimer_restart perf_swevent_hrtimer(struct hrtimer *hrtimer) 
	u64 period;



	event = container_of(hrtimer, struct perf_event, hw.hrtimer);



	if (event->state != PERF_EVENT_STATE_ACTIVE)

		return HRTIMER_NORESTART;



	event->pmu->read(event);



	perf_sample_data_init(&data, 0);
@@ -5628,9 +5632,6 @@ static void perf_swevent_start_hrtimer(struct perf_event *event) 
	if (!is_sampling_event(event))

		return;



	hrtimer_init(&hwc->hrtimer, CLOCK_MONOTONIC, HRTIMER_MODE_REL);

	hwc->hrtimer.function = perf_swevent_hrtimer;



	period = local64_read(&hwc->period_left);

	if (period) {

		if (period < 0)
@@ -5657,6 +5658,30 @@ static void perf_swevent_cancel_hrtimer(struct perf_event *event) 
	}

}



static void perf_swevent_init_hrtimer(struct perf_event *event)

{

	struct hw_perf_event *hwc = &event->hw;



	if (!is_sampling_event(event))

		return;



	hrtimer_init(&hwc->hrtimer, CLOCK_MONOTONIC, HRTIMER_MODE_REL);

	hwc->hrtimer.function = perf_swevent_hrtimer;



	/*

	 * Since hrtimers have a fixed rate, we can do a static freq->period

	 * mapping and avoid the whole period adjust feedback stuff.

	 */

	if (event->attr.freq) {

		long freq = event->attr.sample_freq;



		event->attr.sample_period = NSEC_PER_SEC / freq;

		hwc->sample_period = event->attr.sample_period;

		local64_set(&hwc->period_left, hwc->sample_period);

		event->attr.freq = 0;

	}

}



/*

 * Software event: cpu wall time clock

 */
@@ -5709,6 +5734,8 @@ static int cpu_clock_event_init(struct perf_event *event) 
	if (event->attr.config != PERF_COUNT_SW_CPU_CLOCK)

		return -ENOENT;



	perf_swevent_init_hrtimer(event);



	return 0;

}
@@ -5787,6 +5814,8 @@ static int task_clock_event_init(struct perf_event *event) 
	if (event->attr.config != PERF_COUNT_SW_TASK_CLOCK)

		return -ENOENT;



	perf_swevent_init_hrtimer(event);



	return 0;

}

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